Spinosaurus Was Built for Water, But Scientists Are Still Debating the Details

Picture the most famous predatory dinosaur you know. Chances are you thought of T. rex — the iconic, two-fingered giant with bone-crushing jaws. Now imagine a dinosaur that was arguably even larger, had a crocodile-like snout lined with sharp teeth, a fan-shaped sail rising from its back as tall as an adult human, and legs built more for paddling than sprinting. That is Spinosaurus, and it is one of the most hotly debated animals in all of paleontology — the scientific study of ancient life through fossils. Scientists have been arguing about how this creature actually lived ever since its bones were first described more than a century ago, and new discoveries keep making the picture more complicated.

Spinosaurus aegyptiacus — its full scientific name — stretched over 46 feet from snout to tail, making it comparable in length to the largest meat-eating dinosaurs ever found. German paleontologist Ernst Stromer first described it in 1912 from bones uncovered in Egypt. Those early fossils showed a lower jaw packed with long, conical teeth that looked more like a fish's than a carnivore's, and individual vertebrae — the bones that stack to form a spine — that supported enormous upright spines on its back, clearly forming some kind of sail. Stromer named it Spinosaurus, meaning “spine lizard,” because, well, those spines were impossible to ignore. Then, in 1944, a British air raid on Munich destroyed the original fossils entirely, leaving scientists with nothing but drawings and notes to work from for decades.

New fossils found in Morocco in the 1980s and a major 2014 discovery began to reveal just how strange Spinosaurus truly was. That 2014 partial skeleton showed stubby legs compared to its body size, a tail shaped almost like a paddle due to elongated spines, and bones that were unusually dense — more like the bones of early whales than those of a land-based predator. Dense bones act as ballast, the same way a diver wears a weighted belt to sink more easily rather than bobbing at the surface. All of these features pointed strongly toward an animal that spent significant time in the water, not just wading at the edge of a river but actually swimming through it.

So was Spinosaurus a swimmer or a wader? That is exactly where the scientific debate gets fierce. Paleontologist Matteo Fabbri of Johns Hopkins University, who has studied Spinosaurus behavior closely, says the bulk of the current evidence favors a strong swimmer. Beyond the bone density clue, chemical signals preserved inside Spinosaurus teeth suggest the animal spent more time in the water than other carnivorous dinosaurs did. Spinosaurus fossils are also consistently found alongside the remains of large fish and crocodiles — creatures that lived in deep water, not shallow puddles. Other researchers, though, argue that Spinosaurus was more like a heron — a bird that wades into shallow water to stab at fish rather than diving beneath the surface. “The debate is ongoing,” Fabbri says, and both sides agree that this was an animal deeply connected to water. The disagreement is about just how deep that connection went.

Part of what makes this debate so hard to settle is that no one has ever found a complete Spinosaurus skeleton. Much of what scientists believe about its body — including details about its arms and claws — comes from comparing it with related dinosaurs in the spinosaur family. That family includes roughly two dozen species discovered on almost every continent, from England and Brazil to China and Morocco. They flourished between about 94 million and 140 million years ago. Some spinosaurs, like the “heavy claw” Baryonyx — found in England and famous for a 12-inch hooked claw probably used to snag fish — were more land-based hunters. Others, like Ichthyovenator, whose name literally means “fish hunter,” shared more of Spinosaurus's aquatic features. The group shows that dinosaurs were not limited to the dry-land world most people imagine — some were genuinely at home in prehistoric rivers and coastal waters.

The story keeps evolving. In early 2025, scientists described a brand-new species called Spinosaurus mirabilis, based on a skull with a striking crest found relatively far inland from the prehistoric coastline. Some researchers argue this suggests the new species was more of a shoreline hunter than an open-water swimmer. But paleontologist Andrés Santos-Cubedo of Jaume I University cautions that scientists cannot properly assess any Spinosaurus species' swimming abilities until they find a much more complete skeleton. Better fossils, he explains, would allow researchers to build realistic biomechanical models — computer-based simulations of how an animal's body actually moved — to test the swimming hypothesis properly. Until that day comes, Spinosaurus will remain one of dinosaur science's most compelling, unresolved questions, a creature whose fame has always run ahead of what we truly know.

Source: Smithsonian Magazine